1. Field of the Invention
In one of its aspects, the present invention relates to a radiation source assembly. In another of its aspects, the present invention relates to a radiation source module comprising a novel radiation source assembly having incorporated therein an optical radiation sensor.
2. Description of the Prior Art
Optical radiation sensors are known and find widespread use in a number of applications. One of the principal applications of optical radiation sensors is in the field of ultraviolet radiation fluid disinfection systems.
It is known that the irradiation of water with ultraviolet light will disinfect the water by inactivation of microorganisms in the water, provided the irradiance and exposure duration are above a minimum “dose” level (often measured in units of microwatt seconds per square centimeter). Ultraviolet water disinfection units such as those commercially available from Trojan Technologies Inc. under the tradenames Trojan UV MaX™, Trojan UV Logic™ and Trojan UV Swift™, employ this principle to disinfect water for human consumption. Generally, water to be disinfected passes through a pressurized stainless steel cylinder which is flooded with ultraviolet radiation. Large scale municipal waste water treatment equipment such as that commercially available from Trojan Technologies Inc. under the trade-names UV3000™, UV3000 Plus™ and UV4000™, employ the same principle to disinfect waste water. Generally, the practical applications of these treatment systems relates to submersion of a treatment module or system in an open channel wherein the wastewater is exposed to radiation as it flows past the lamps. For further discussion of fluid disinfection systems employing ultraviolet radiation, see any one of the following:                U.S. Pat. No. 4,482,809,        U.S. Pat. No. 4,872,980,        U.S. Pat. No. 5,006,244,        U.S. Pat. No. 5,418,370,        U.S. Pat. No. 5,539,210, and        U.S. Pat. No. Re36,896.Most commercially available ultraviolet radiation fluid treatment systems employ so-called low pressure (including low pressure/high output) lamps (e.g., such systems available from Trojan Technologies Inc. under the trade-names UV3000™ and UV3000 Plus™) or medium pressure lamps (e.g., such systems available from Trojan Technologies Inc. under the trade-name UV4000™).        
In many applications, it is desirable to monitor the level of ultraviolet radiation present within the water under treatment. In this way, it is possible to assess, on a continuous or semi-continuous basis, the level of ultraviolet radiation, and thus the overall effectiveness and efficiency of the disinfection process.
It is known in the art to monitor the ultraviolet radiation level by deploying one or more passive sensor devices near the operating lamps in specific locations and orientations which are remote from the operating lamps. These passive sensor devices may be photodiodes, photoresistors or other devices that respond to the impingement of the particular radiation wavelength or range of radiation wavelengths of interest by producing a repeatable signal level (in volts or amperes) on output leads.
Conventional passive sensor devices (e.g., photodiodes, photoresistors and the like) used to monitor ultraviolet radiation levels are responsive to light according to the light absorbing properties of the active material in the sensor. For example, silicon-based detectors commonly used in light detection are responsive to light over the range of from about 125 nm to about 1100 nm. This range of sensitivity encompasses many types of radiation and is much larger than needed to detect radiation in the ultraviolet region—i.e., radiation having at least one wavelength in the range of less that about 300 nm, ideally from about 240 nm to about 290 nm for disinfection and/or from about 175 to about 300 nm for treatment of chemical contaminants. The term “treatment of contaminants” is intended to mean reduction of the concentration of one or more contaminants in the water —in some cases, it can result in complete removal of the contaminant.
The use of such conventional passive sensor devices can result in inaccurate irradiance values in a disinfection system if a broad range of radiation is present in the disinfection system—i.e., radiation falling broadly in the range of from about 290 nm to about 1100 nm. Conventional silicon-based sensors also suffer from degradation in performance when exposed to the high intensity ultraviolet radiation used for prolonged periods of time in fluid treatment and/or disinfection systems.
A relatively recent development in the art of ultraviolet radiation fluid treatment systems is the use of a silicon carbide (SiC) detector as a sensing device. The relatively large bandgap of SiC narrows the wavelength range over which the detector is sensitive—i.e., to a wavelength range of from about 220 nm to about 400 nm. Thus, the SiC detector is relatively insensitive to radiation having at least one wavelength greater than about 400 nm. In turn, this can reduce the likelihood that the above-mentioned measurement error will occur. More information on this application of SiC detectors may be found in U.S. Pat. No. 6,057,917 [Petersen et al.] and U.S. patent application publication 2002/162,970 [Sasges].
An emerging application of fluid treatment systems which utilize medium pressure mercury lamps is the removal of chemical contaminants and dissolved organic carbon in water. Ultraviolet radiation having a wavelength in the range of from about 175 nn to about 300 nm is suitable for this application, where the exact wavelength range depends on the specific application. Unfortunately, silicon carbide is only responsive to radiation having a wavelength of greater than about 220 nm and thus a sensor device using SiC is not well suited for monitoring UV light intensity in the lower wavelength range for applications such as chemical contamination removal.
U.S. Pat. No. 6,611,375 [Knapp] teaches selectively tuned ultraviolet optical filters and methods of use thereof. More specifically, Knapp teaches optical filters that purportedly are tuned specifically for ultraviolet water purification, and, as such, these optical filters are said to be characterized by: (i) transmitting effectively within the wavelengths that contribute to ultraviolet sterilization (centered at 254 nm); (ii) selectively rejecting those background discrete wavelengths in the UV/VIS/IR emission spectra of typical mercury lamps and which fall within the sensitivity region of photodiodes; and (iii) are resistant to damage from high intensity ultraviolet radiation. More, particularly, Knapp teaches optical filters having: (i) an optical transmittance of at least about 40%, more preferably at least about 70%, still more preferably at least about 75% or 79% at a wavelength of about 254 nm, and (ii) an optical transmittance of no greater than 5% at wavelengths of 313 nm to 580 nm and 1000 nm to 1140 nm. The profile of a sensor device employing such an optical filter is illustrated in FIG. 11 of Knapp—this Figure illustrates that the optical filter of Knapp allows radiation having a wavelength in the range of from about 600 nm to about 950 nm to pass therethrough. Unfortunately, even radiation having a wavelength in the range of from about 600 nm to about 950 nm can result in inaccurate irradiance values for conventional silicon-based photodiodes—this issue is not addressed or otherwise dealt with in the teachings of Knapp.
Thus, despite the advances made in the art, there is room for improvement. Specifically, it would be desirable to have a radiation sensor device (particularly for use in ultraviolet radiation fluid treatment systems) capable of detecting and responding to radiation having at least one wavelength in the range of from about 175 nm to about 350 nm while avoiding the disadvantages of the prior art.